Fix the fuel flow indication and things may get a lot easier. Most of us get grouchy at display dithering of 0.2, and you're over 1 GPH in steady state cruise.
Van's Air Force
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Engine stumble
- Thread starter crabandy
- Start date
Fix the fuel flow indication and things may get a lot easier. Most of us get grouchy at display dithering of 0.2, and you're over 1 GPH in steady state cruise.
Right after I get that intake valve fixed!
Well, seems the culprit is a "gummed" up exhaust valve...
Sorry for the poor attempt at humor, trying to keep on the sunny side.
The intake valve on #2 seems to be working fine, the exhaust however wins the award for the most stuck my A&P has tapped with a mallet. Working the valve in with light mallet taps and out with the rope in the cylinder back and forth over 50 times with penetrating oil/lubricant didn't seem to loosen it up. Also, The exhaust valve never seemed to fully seat. The best we could tell the valve stem measured .4935, and the valve guide measured .4935. No gouges, scratches or deposit buildups that we could find. We weren't ever able to get the valve seated enough for any sort of compression test on #2, we did get 79/80 on the other three cylinders.
Because of the way the exhaust valve never fully seats, and the availability of a suitable reamer I think we are going to pull the #2 cylinder and have a cylinder repair shop fix it. I want to check the condition of the valves of the other cylinders tomorrow before pulling the #2 cylinder to verify the condition of the other valves.
I did do some calling around and couldn't find anyone with a suitable reamer except for sky geek, it was almost $1000. Any ideas where to find a piloted valve guide reamer .4975-.4985?
Sorry for the poor attempt at humor, trying to keep on the sunny side.
The intake valve on #2 seems to be working fine, the exhaust however wins the award for the most stuck my A&P has tapped with a mallet. Working the valve in with light mallet taps and out with the rope in the cylinder back and forth over 50 times with penetrating oil/lubricant didn't seem to loosen it up. Also, The exhaust valve never seemed to fully seat. The best we could tell the valve stem measured .4935, and the valve guide measured .4935. No gouges, scratches or deposit buildups that we could find. We weren't ever able to get the valve seated enough for any sort of compression test on #2, we did get 79/80 on the other three cylinders.
Because of the way the exhaust valve never fully seats, and the availability of a suitable reamer I think we are going to pull the #2 cylinder and have a cylinder repair shop fix it. I want to check the condition of the valves of the other cylinders tomorrow before pulling the #2 cylinder to verify the condition of the other valves.
I did do some calling around and couldn't find anyone with a suitable reamer except for sky geek, it was almost $1000. Any ideas where to find a piloted valve guide reamer .4975-.4985?
Although I wouldn't talk you out of pulling your #2 cylinder and bore scoping the rest of them, I think reaming the guide would be exactly the cure for your problem (based on the measurements provided above)
If there is no carbon build up as you stated then someone did not properly ream that valve guide as recommended by Lycoming.
Don't know the precise numbers for your engine but ballpark clearance between valve guide and stem is somewhere between .015 and maximum .030
Zero clearance without carbon build up makes the case pretty clear.
Glad you found your problem, let us know how it ends.
Mind telling how you determined the intake was fine?
BillL
Well Known Member
Glad you got to the bottom of it. At least hopefully it is the bottom.
A reamer is a reamer. A good machine shop will cut one for you to what ever you want. I suspect it does have carbon in there, as it can get very hard. (diamonds, remember)
Regardless of the reamer, popping the jug and further inspection is a good thing. Just don't put silicone for a base gasket sealer!
"Off with it's head . . . " I like that comment.
BillL
Well Known Member
Note that the intake valve is not rotating either. Look at the wear on the top of the stem.
My sentiments exactly. Without pulling the cylinder and removing both valves and inspecting and measuring with the proper tooling, you can only guess as to the condition of the valves, guides, seats etcetera.
cajunwings
Well Known Member
Valve trouble
Make sure you have the correct bushings in the rocker arms. The exhaust rocker has the oil passage. I've seen where the engine builder incorrectly re-bushed all rocker arms with the solid bushings and also where the engine assembler had the correct parts but incorrectly installed the exhaust rocker on the intake side and intake rocker on the exhaust side. End result is less lube and cooling for the exhaust valve leading to accelerated wear and other issues.
Don B
RV 9 Rebuild in Progress.
Make sure you have the correct bushings in the rocker arms. The exhaust rocker has the oil passage. I've seen where the engine builder incorrectly re-bushed all rocker arms with the solid bushings and also where the engine assembler had the correct parts but incorrectly installed the exhaust rocker on the intake side and intake rocker on the exhaust side. End result is less lube and cooling for the exhaust valve leading to accelerated wear and other issues.
Don B
RV 9 Rebuild in Progress.
I really should have emphasized the "Seems" alright on my last post. We didn't do any in depth checking of the intake valve, it is still highly suspect due to DanH's analysis of the engine data.
The intake valve seemed to operate normally while turning the prop and watching the valve movement, removing the rocker arm and tapping the valve stem with a mallet resulted in a "ring" that the valve was contacting the seat. The exhaust valve, not so much. Since the cylinder is going to come off we'll take a closer look at the intake valve while it's off.
I'm hoping once we get the cylinder off we'll find out if it's installation or operator error.
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I believe it's just the picture, closer inspection later.
Mike S
Senior Curmudgeon
Does the intake even have a rotator?
I am used to seeing them on exhaust valves, not intakes.
But, I am used to auto engines, not aircraft.
kkmarshall
Well Known Member
"Rope trick"
To each his own,but the FULL rope trick is absolutely a fix for this problem. I have done a couple of Lyc 540's and reamed all exhaust guides w/o pulling any cylinders. First cyl will take an hour or so & then when you get a feel for it you can do a cyl in about 30-45 mins. You can find pics on the web. Pull both plugs,get a strong telescoping magnet that is smaller than the ex guide and tap the ex valve completely into the cyl with piston at bottom dead center. Kinda scarey on the first one but amazingly easy to fish the valve back in the guide once properly reamed. You can even fish the valve stem out the bottom plug hole and polish the stem of carbon. Works like a charm.
Keith
To each his own,but the FULL rope trick is absolutely a fix for this problem. I have done a couple of Lyc 540's and reamed all exhaust guides w/o pulling any cylinders. First cyl will take an hour or so & then when you get a feel for it you can do a cyl in about 30-45 mins. You can find pics on the web. Pull both plugs,get a strong telescoping magnet that is smaller than the ex guide and tap the ex valve completely into the cyl with piston at bottom dead center. Kinda scarey on the first one but amazingly easy to fish the valve back in the guide once properly reamed. You can even fish the valve stem out the bottom plug hole and polish the stem of carbon. Works like a charm.
Keith
Russ McCutcheon
Well Known Member
My trusted A&P/engine guy has his own reamer for this, if yours doesn't I would find more help before pulling the jug.
az_gila
Well Known Member
If the cylinder has been pulled, I would skip the "A&P with a reamer" and take it to an engine rebuild shop...
JonJay
Well Known Member
Congrats on finding the issue. Obviously you're going to get varying opinions on the next step, none necessarily wrong.
I chose to pull mine when #2 exhaust valve stuck. #2 is a whole lot easier to pull than #3 or #4. Most of the time is invested in the baffle.
When you are done with whatever path you take, you will want to recheck your idle mixture and rpm's. I would be surprised if you where able to set them correctly to start with. A stuck exhaust valve can cause havoc at idle.
I chose to pull mine when #2 exhaust valve stuck. #2 is a whole lot easier to pull than #3 or #4. Most of the time is invested in the baffle.
When you are done with whatever path you take, you will want to recheck your idle mixture and rpm's. I would be surprised if you where able to set them correctly to start with. A stuck exhaust valve can cause havoc at idle.
kkmarshall
Well Known Member
Rotator
Not aware of any intake rotators on these engines.
I surely wouldn't pull the jug,just ream the guide. As someone mentioned,a machine shop would likely have a reamer. Reaming in place is a Lycoming approved procedure. WAY easier than pulling a jug.
Keith
Not aware of any intake rotators on these engines.
I surely wouldn't pull the jug,just ream the guide. As someone mentioned,a machine shop would likely have a reamer. Reaming in place is a Lycoming approved procedure. WAY easier than pulling a jug.
Keith
Not trying to start an argument here, just being Captain Obvious....tapping a stuck valve, or "staking a valve" or "doing the rope trick" to "free up a valve" IS NOT a fix for anything. If a valve is sticking due to "excessive carbon" it is because the valve guide is worn beyond limits and has excessive clearance. A valve giude that is in tolerance will not "carbon up" or cause sticking issues. "Reaming a valve guide", or the more accurately described process of passing a ream through a valve guide to remove carbon is not a fix for a problem either. Both of these "fixes" will often make a cylinder run normally for a brief time. The big questions are how long will it run correctly, and what damage has been done to the valve, guide and seat already.
In the past I have had several friends who have experianced an intermittant power loss and asked me to "stake a valve" becuase someone told them that was the easy and inexpensive fix. I refused every time and explained that it is a temporary fix at best, and could possibly result in a complete cylinder failure or worse. Every time these owners elected to have another mechanic "stake the valve" and every time the problem came back in a short period of time. One of my friends was flying his O-320 powered C-172 over a planted pine tree forrest at gross weight with his entire family aboard the last time the exhaust valve stuck on cylinder #4 and he lost a considerable amount of altitude before the engine regained enough power to climb again. After he fessed up and told me he had the valve "staked" three times already and didn't have the money to fix it at the time, I offered to do the labor for free. When we removed the #4 cylinder we found the exhaust valve was burned as well as a scorched piston adjacent to the exhaust valve. We sent the cylinder assembly to Don George for repair. Don called a few days later and said the exhaust valve was severly burnt and that he was suprised that either the valve head or the piston dome above the ring land didn't seperate. Had either of these failures occured the best case scenario would have been a "holed piston"...the worst could have been a complete cylinder seperation that resulted in a case failure. Continuing to band aid a sticking valve instead of addressing and correcting the root cause may ultimately cost way more that the few hundred dollars that it will cost for a cylinder shop to fix cylinder correctly.
In the past I have had several friends who have experianced an intermittant power loss and asked me to "stake a valve" becuase someone told them that was the easy and inexpensive fix. I refused every time and explained that it is a temporary fix at best, and could possibly result in a complete cylinder failure or worse. Every time these owners elected to have another mechanic "stake the valve" and every time the problem came back in a short period of time. One of my friends was flying his O-320 powered C-172 over a planted pine tree forrest at gross weight with his entire family aboard the last time the exhaust valve stuck on cylinder #4 and he lost a considerable amount of altitude before the engine regained enough power to climb again. After he fessed up and told me he had the valve "staked" three times already and didn't have the money to fix it at the time, I offered to do the labor for free. When we removed the #4 cylinder we found the exhaust valve was burned as well as a scorched piston adjacent to the exhaust valve. We sent the cylinder assembly to Don George for repair. Don called a few days later and said the exhaust valve was severly burnt and that he was suprised that either the valve head or the piston dome above the ring land didn't seperate. Had either of these failures occured the best case scenario would have been a "holed piston"...the worst could have been a complete cylinder seperation that resulted in a case failure. Continuing to band aid a sticking valve instead of addressing and correcting the root cause may ultimately cost way more that the few hundred dollars that it will cost for a cylinder shop to fix cylinder correctly.
kkmarshall
Well Known Member
Absolutely agree that " staking a valve " or just freeing a valve is no fix at all. I will respectfully disagree that a guide that is well within service limits will not carbon up. Lycoming service bulletins also make that clear but it is certainly fine if the OP elects to pull the cylinder. I was simply offering a much less labor intensive fix that is indeed factory authorized. No offense taken or intended towards anyone.
Keith
Keith
Russ McCutcheon
Well Known Member
Also less invasive,,,, the less you take apart the less chances for mistakes. And yes you are correct they can carbon up when there well in limits.
So there I am pulling the spring retainer off #2 intake valve, I see my college roomate's dad Jim on landing roll-out in his GlasAir. He flew up to check out the new landing gear on a friends Cassut.
#2 intake as well as both valves on #4 felt good sliding in/out/twisting in the valve guide with the spring removed. Valve twisting on the seat was a tad rough, maybe use some lapping compound. I'm piddling with valves and Jim asks, why is the engine so dirty, how many hours, what oil, do you even change the oil? Aeroshell 100 mineral changes at roughly 10-30-50hours and I switchd to Aeroshell 100 plus just turned about 90 and I drained it again. Oil usage? Well hard to track precisely, it seems to blow anything above 5 1/2 out the breather but 3-7 hours a quart.
"How long did you run it on the ground before you flew it? Were you at low power? 45-60 minute total ground running but CHT's never topped 325 ish before I shut it down and cooled it off. First 10 hours I was surprised flight after flight for 10 hours that an O-360 burned 16.5 gallons an hour down low at full throttle, I flew it harder than a Wet Rental. See where this is going?
"Well regardless your rings never seated." That painted the picture pretty clear for me. I'm the third owner of my field overhauled engine, long story short I had suspicions that the engine had been installed and flown despite the "new" logbook and overhaul endorsement.
My guess is the cylinders were glazed before I got it, CHT's and oil usage dropped a little after 7 hours but not much. From what I could find online/in person was that chrome cylinders used more oil than steel cylinders and 3-7 quarts of oil an hour was still an accepted usage amount.
That made the decision to pull all the cylinders pretty easy, another 3-4 hours and I'll be ready to pull them. I'm going to take the cylinders to a shop and decide where to go from there, good news is I'll get to take a peek at the bottom end. I'm sure I could ream the 1 guide and keep pouring oil in it, but it's just another problem waiting to happen in this case.
Thanks again for everyone's input, I don't know what I don't know!
#2 intake as well as both valves on #4 felt good sliding in/out/twisting in the valve guide with the spring removed. Valve twisting on the seat was a tad rough, maybe use some lapping compound. I'm piddling with valves and Jim asks, why is the engine so dirty, how many hours, what oil, do you even change the oil? Aeroshell 100 mineral changes at roughly 10-30-50hours and I switchd to Aeroshell 100 plus just turned about 90 and I drained it again. Oil usage? Well hard to track precisely, it seems to blow anything above 5 1/2 out the breather but 3-7 hours a quart.
"How long did you run it on the ground before you flew it? Were you at low power? 45-60 minute total ground running but CHT's never topped 325 ish before I shut it down and cooled it off. First 10 hours I was surprised flight after flight for 10 hours that an O-360 burned 16.5 gallons an hour down low at full throttle, I flew it harder than a Wet Rental. See where this is going?
"Well regardless your rings never seated." That painted the picture pretty clear for me. I'm the third owner of my field overhauled engine, long story short I had suspicions that the engine had been installed and flown despite the "new" logbook and overhaul endorsement.
My guess is the cylinders were glazed before I got it, CHT's and oil usage dropped a little after 7 hours but not much. From what I could find online/in person was that chrome cylinders used more oil than steel cylinders and 3-7 quarts of oil an hour was still an accepted usage amount.
That made the decision to pull all the cylinders pretty easy, another 3-4 hours and I'll be ready to pull them. I'm going to take the cylinders to a shop and decide where to go from there, good news is I'll get to take a peek at the bottom end. I'm sure I could ream the 1 guide and keep pouring oil in it, but it's just another problem waiting to happen in this case.
Thanks again for everyone's input, I don't know what I don't know!
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I especially want to thank DanH for taking the time and effort for his (IMHO) excellent analysis of my engine data.
Even though I removed the valve spring and everything "felt" good on the #2 intake, it is still highly suspect because of Dan's analysis. I've made way more than my fair share of mistakes before and will be looking especially hard at the #2 intake from the valve/seat to the cam.
Even though I removed the valve spring and everything "felt" good on the #2 intake, it is still highly suspect because of Dan's analysis. I've made way more than my fair share of mistakes before
and will be looking especially hard at the #2 intake from the valve/seat to the cam.I would like to see one of the engine builders weigh in on what they think about perfectly good valves and guides seizing up due to carbon accumulation. If this was reality everyone that owned a Lycoming would be "reaming" exhaust guides every few hundred hours as preventative maintenance. I work on quite a few piston aircraft each year and never have to "ream" exhaust guides to keep engines running.
As far as the less you take apart the less chances for mistakes goes....when an engine is broken and does not run correctly, I prefer to disassemble the engine to such extent necessary to identify and correct the root cause, not address the symptom and just make it run one more time. Besides if you cannot remove and reinstall a cylinder on an aircraft engine without making mistakes and causing potential problems or damage, then maybe you should get some qualified help.
Russ McCutcheon
Well Known Member
Qualified help is the person who most often makes the mistake, in any case I think crabandy has a plan and it sounds like a good one.
FWIW, the reaming/measuring procedure is recommended after a 1000 hours if I'm not mistaken.
Mike, how long in your experience does it take for a sticking valve to reoccur after reaming? I've had a badly stuck exhaust valve approximately 60 hours ago, and a mechanic from an overhaul shop reamed the guide and measured its ID (which was fine). It has been running fine since. I'm wondering if I should expect this to happen again soon.
This is the million dollar question, and I do not have a good answer for you. I have only decarboned a few exhaust valve guides with reamers in the past, but every one of those cylinders ended up having recurring valve sticking issues, most of which reoccurred in less than 100 hours. If you were able to obtain an accurate measurement of the guide, and also performed a thorough visual inspection of all of the related valve train components and found that there were no other issues, then maybe in you're case "reaming" the guide to remove the carbon was the right thing to do.
The point I am trying to make is that while it is possible to have a circumstance where a cylinder with a serviceable valve guide will experience valve sticking due to valve guide carbon build up, it is definitely not the norm despite what some mechanics and owners would like everyone to believe. I feel that the "staking the valve" and "rope trick" "fixes" that some mechanics/owners perform on a regular basis are most likely a result of the mechanic not understanding how to troubleshoot and diagnose the root cause, or because they are lazy and do not want to pull the cylinder and fix the problem, and instead just want to make the problem go away right now, or they do not want to have the difficult discussion with the owner that a cylinder needs to be removed and sent out for inspection and repair. As I have stated before beating on a valve stem or “reaming “ a guide and expecting that to correct the condition that is causing a sticking valve is nonsense and these “fixes” have been perpetuated for far too long.
I have spoken with several engine rebuilders and cylinder shop owners and technicians concerning valve guide wear and valve sticking in the past. All of them have told me that an exhaust valve guide will be worn beyond the limits stated in the overhaul manual within the first 150-200 hours of operation. This data point can also be confirmed by looking at the notes in the cylinder wear limits table, section II, item 615 of Lycoming document SSP 1776. Having said that, it is fully expected than an engine will operate normally with the exhaust valve guide worn up to and possibly beyond .015” over the nominal limits listed in the overhaul manual. Wear in excess of these “service limit” tolerances will definitely contribute to valve sticking.
Lycoming Service Instruction Letter 1425A does in fact describe how to decarbon an exhaust valve guide, but nowhere in this document does it imply that this is a “normal procedure” in fact it goes on to describe multiple conditions and scenarios that contribute to valve sticking. Furthermore SI 1425A has you actually measure the exhaust valve guide to help determine serviceability of the guide. Nowhere in SI 1425A does it call out to beat on the valve stem to free up a valve, nor does it say to stuff a rope in the cylinder to force a stuck valve closed. This Service Instruction Letter actually has you inspect the valve train for condition and serviceability, not just simply hog out the carbon and slap it back together. I would even wager that most mechanics that perform this procedure never measure the guide, nor do they have access to a set of Go/No Go pin gauges. Additional problems/conditions that are not even addressed by SI1425A are valve and piston condition. As I previously stated I have seen an engine that was run for a prolonged period of time with a sticking exhaust valve that resulted in a severely burnt valve and scorched piston. Both the valve and piston were on the verge of failure due to this thermal distress, and had the engine been operated very much longer, it would have experienced a failure. Identifying a burnt exhaust valve and or a scorched piston takes a trained eye, and when a cylinder is still installed on an engine it often takes a very expensive borescope as well.
The most recent valve sticking issue that I have helped troubleshoot occurred on an O-200. This particular O-200 was recently overhauled less than 50 hours ago due to camshaft corrosion/failure that resulted in stuck valves and intermittent lifter collapse due to oil contamination. This engine was overhauled using overhauled cam/lifters/tappet bodies and new cylinder assemblies, then less than 50 hours later the owner reported similar issues. At least three pilots and two mechanics tried to “troubleshoot” the problem with no success. A quick oil check and compression check revealed a stuck exhaust valve on cylinder 4, and severely contaminated oil. The oil was silver in color and contained lots of reflective “sparkles” A quick look in the bore of the cylinders confirmed that the Cermanil coating was peeling off of the cylinder walls. One of the mechanics who was previously involved with “troubleshooting” this issue recommended to “stake” the exhaust valve.
I have spent entirely too much time typing out this diatribe. My goal is not to start an argument or fuel a never ending debate, but to provide anther data point that contradicts the endless perpetuation of these “quick fixes” and to help pilots, owners and mechanics determine the best course of action to correct a sticking valve before it becomes a safety issue.
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Man that escalated quickly...
Well, she's jug less...
Inside #2, the exhaust valve has a little powdery yellow residue that wasn't present in the other cylinders.
Onto the cylinder shop with the top end, hopefully a couple pairs of trained eyes to check out the bottom end.
Well, she's jug less...
Inside #2, the exhaust valve has a little powdery yellow residue that wasn't present in the other cylinders.
Onto the cylinder shop with the top end, hopefully a couple pairs of trained eyes to check out the bottom end.
You're thinking the rings never seated?
Right. I bet those plugs are always black. Probably high oil consumption and black oil. Maybe leaky externally too from blowby. The other cylinders may be headed there also. Usually spark plug color will confirm all this. Upside is a normal lap through a cylinder shop and new rings combined with some dirty fingernails can make it all go away.
BillL
Well Known Member
Great thread Andy, sorry it will cost so much, but it certainly is helpful to educate the population on some of the internal workings. It should be said that there is a quite a bit of difference in nitrided steel, chrome plated, and ceramic coated cylinder walls.
Hopefully, you can get flying again soon.
Hopefully, you can get flying again soon.
You previously said "We weren't ever able to get the valve seated enough for any sort of compression test on #2." So what did the seat area and seat ring look like, and was the head bent?
Kinda hoped you would make some simple measurements before it went off.
This is a ball gauge. They're used in concert with a good micrometer. Common as dirt.
Measure the guides in the plane of the rocker arm centerline, then perpendicular to the rocker arm centerline (in the axis of the rocker arm pin), three places for each measurement; near the spring end, halfway through the guide, and near the port end.
With the same micrometer, measure the valve stem diameter in the general area of the three locations. Subtract the stem diameters from the guide diameters, and you know the real clearance at each location, in and out of plane. One or both ends will generally have more clearance than the middle when measured in-plane because of rocker arm forces. Out-of-plane may or may not show much wear. The center may or may not be tight.
You previously said "We weren't ever able to get the valve seated enough for any sort of compression test on #2." So what did the seat area and seat ring look like, and was the head bent?
Kinda hoped you would make some simple measurements before it went off.
This is a ball gauge. They're used in concert with a good micrometer. Common as dirt.
Measure the guides in the plane of the rocker arm centerline, then perpendicular to the rocker arm centerline (in the axis of the rocker arm pin), three places for each measurement; near the spring end, halfway through the guide, and near the port end.
With the same micrometer, measure the valve stem diameter in the general area of the three locations. Subtract the stem diameters from the guide diameters, and you know the real clearance at each location, in and out of plane. One or both ends will generally have more clearance than the middle when measured in-plane because of rocker arm forces. Out-of-plane may or may not show much wear. The center may or may not be tight.
Sure thing, I was in a bit of a hurry to get things removed before work! I'll do some playing around the next couple days. Great illustrations on what to measure and where.
We did make a couple of measurements on the stuck exhaust valve stem and the outside portion of the guide. Both the stem and the guide measured .4935, which is correct for the valve stem but doesn't give the required clearance of .0040-.0060 in the guide.
Online service limits, my A&P friend said the "S" denoted the parallel valve (it's usually grouped with several letters like GJ-S-T-BD-BE):
http://www.7ts0.com/manuals/lycoming/STL_TVR.pdf
I honestly haven't decided if I'm going to have the cylinders re-worked yet or not. Numerous things I don't like about the current cylinders/workmanship, I may be money ahead buying new. I also plan on getting several sets of eyes on the bottom end.
I previously mentioned NTSB #NYC99LA173, which is interesting.
http://www.ntsb.gov/_layouts/ntsb.aviation/brief2.aspx?ev_id=20001212X19342&ntsbno=NYC99LA173&akey=1
Fine example of the sort of report which drives me nuts. The investigator wastes space telling us exactly how the pilot conducted the doomed flight, but expends no effort to examine the underlying poor maintenance practice which killed the engine in the first place.
Note that (1) the engine suffered morning sickness, (2) but the subsequent failure was an intake rocker, and (3) it never mentions which valve the mechanic "repaired".
http://www.ntsb.gov/_layouts/ntsb.aviation/brief2.aspx?ev_id=20001212X19342&ntsbno=NYC99LA173&akey=1
Fine example of the sort of report which drives me nuts. The investigator wastes space telling us exactly how the pilot conducted the doomed flight, but expends no effort to examine the underlying poor maintenance practice which killed the engine in the first place.
Note that (1) the engine suffered morning sickness, (2) but the subsequent failure was an intake rocker, and (3) it never mentions which valve the mechanic "repaired".
If the valve that was forced closed using the rope trick was the intake, that may explain the broken intake rocker arm. Forcing a valve closed on an engine that uses hydraulic lifters usually results in bent push rods, bent valve stems, bent or cracked rocker arms or sheared rocker shafts or bolts if the push rod was not removed.
Looks like the rope trick "fixed" this guys 172 really good.
Looks like the rope trick "fixed" this guys 172 really good.
No luck on the ball guage, unfortunately most everything must be ordered online nowadays.
Valve stem measured in 6 spots as DanH suggested, best I could measure with my el Cheapo caliper was .4935 in all six spots. More knowledgable eyes and tools for a better analysis later.
The valve guide looked like it still had reamer marks in it, and just a hair bit of carbon. It looked like a shotgun barrel that had been fired once since it was cleaned.
Exhaust valve seat is pitted, it seems like a slightly broader wear/seat surface at the 6-9 o'clock position and narrower at the 1-3 o'clock position.
Another thing that really bothered me was the bushings on the rocker arms and rocker arm bosses. Most have scratches/dings from what looks like disassembly and installation with a flat blade screwdriver. Are the bushings not a normal overhaul item on the cylinders? Not the best pic,
The base of one cylinder has 2 dressing marks like the cylinder was dropped on a shop floor and dressed out like a nick in the prop....
Valve stem measured in 6 spots as DanH suggested, best I could measure with my el Cheapo caliper was .4935 in all six spots. More knowledgable eyes and tools for a better analysis later.
The valve guide looked like it still had reamer marks in it, and just a hair bit of carbon. It looked like a shotgun barrel that had been fired once since it was cleaned.
Exhaust valve seat is pitted, it seems like a slightly broader wear/seat surface at the 6-9 o'clock position and narrower at the 1-3 o'clock position.
Another thing that really bothered me was the bushings on the rocker arms and rocker arm bosses. Most have scratches/dings from what looks like disassembly and installation with a flat blade screwdriver. Are the bushings not a normal overhaul item on the cylinders? Not the best pic,
The base of one cylinder has 2 dressing marks like the cylinder was dropped on a shop floor and dressed out like a nick in the prop....
Crabandy,
if you're cylinders require an overhaul it very well may be economicially feasible to just buy new assemblies. If during inspection it is found that a cylinder needs new valves, guides, pistons and rings then the cost for the overhaul will usually be in the $600-$800 dollar range each. When a new cylinder assembly with piston and rings costs $1000-$1200 the cost savings looks pretty marginal. Also keep in mind that the aluminum cylinder heads will only tolerate so many heat cycles before cracks develop. How many hours and heat cycles will a cylinder head last? I have never seen any published data regarding cylinder head life, but most cylinder heads that I have found to be cracked have usually been overhauled at least twice with who knows how many hours on them.
On the other hand if the cylinders just need a guide or two and some new rings and a hone, then a repair, instead of an overhaul may be the way to go.
if you're cylinders require an overhaul it very well may be economicially feasible to just buy new assemblies. If during inspection it is found that a cylinder needs new valves, guides, pistons and rings then the cost for the overhaul will usually be in the $600-$800 dollar range each. When a new cylinder assembly with piston and rings costs $1000-$1200 the cost savings looks pretty marginal. Also keep in mind that the aluminum cylinder heads will only tolerate so many heat cycles before cracks develop. How many hours and heat cycles will a cylinder head last? I have never seen any published data regarding cylinder head life, but most cylinder heads that I have found to be cracked have usually been overhauled at least twice with who knows how many hours on them.
On the other hand if the cylinders just need a guide or two and some new rings and a hone, then a repair, instead of an overhaul may be the way to go.
Thanks Mike.
I'm going to have the cylinders evaluated by a cylinder shop, if they need much work they are going to become decorations. Possibly I can bring my current cylinders up to snuff and they will have some value. I'm really leaning toward factory Lycoming cylinders regardless.
I'm trying to get a couple opinions on Sat looking at the bottom end, oil filter etc. I just have lots of unanswered questions about the engines true history.
Not sure I want to hang brand new jugs on my bottom end without going through it.
At this point I'm looking for several very good reasons not to pull the bottom end apart.
I'm going to have the cylinders evaluated by a cylinder shop, if they need much work they are going to become decorations. Possibly I can bring my current cylinders up to snuff and they will have some value. I'm really leaning toward factory Lycoming cylinders regardless.
I'm trying to get a couple opinions on Sat looking at the bottom end, oil filter etc. I just have lots of unanswered questions about the engines true history.
Not sure I want to hang brand new jugs on my bottom end without going through it.
At this point I'm looking for several very good reasons not to pull the bottom end apart.
If there is no evidence of corrosion related issues such as mild to severe pitting on the cam, tappet bodies and accessory gears, and the engine made good oil pressure then it will most likely live for a while.
Did the engine have any documentation such as 8130-3 tags or "yellow Tags" indicating that the crankshaft, camshaft, rods and other steel parts were magnafluxed and inspected?
What is the visual condition of the cam and lifter bodies? Are they pitted or spalled? Do any of the lobes show appreciable wear at the lobe peaks?
What do the cylinder deck surfaces on the case look like? Are the smooth and flat, or are they worn, pitted and have fretting wear?
The bottom end of a Lycoming is pretty tough and even when there are issues it usually does not cause catastrophic failure and gives you lots of warning, with the exception of crankshaft and connecting rod/bolt failure.
Did the engine have any documentation such as 8130-3 tags or "yellow Tags" indicating that the crankshaft, camshaft, rods and other steel parts were magnafluxed and inspected?
What is the visual condition of the cam and lifter bodies? Are they pitted or spalled? Do any of the lobes show appreciable wear at the lobe peaks?
What do the cylinder deck surfaces on the case look like? Are the smooth and flat, or are they worn, pitted and have fretting wear?
The bottom end of a Lycoming is pretty tough and even when there are issues it usually does not cause catastrophic failure and gives you lots of warning, with the exception of crankshaft and connecting rod/bolt failure.
Only paperwork I received was the endorsement in the logbook, and yellow tags for the carb and magneto.
This engine may have possibly been installed on an aircraft, had a wood prop-strike and returned for a prop strike inspection (I'm thinking this is when the cylinders became glazed). Cylinders removed leaving pistons/rings in the cylinders and the crankshaft magnafluxed and reassembled with the previous bearings and hardware. No endorsement of the prop-strike inspection.
This engine may have possibly been installed on an aircraft, had a wood prop-strike and returned for a prop strike inspection (I'm thinking this is when the cylinders became glazed). Cylinders removed leaving pistons/rings in the cylinders and the crankshaft magnafluxed and reassembled with the previous bearings and hardware. No endorsement of the prop-strike inspection.
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Possibly. Or the mechanic assumed morning sickness was a stuck exhaust and never looked at the intake. It's an entirely human habit....find something, stop looking.
Along the same lines, the investigator may have seen the broken intake rocker...and never looked for a bent exhaust pushrod, the smoking gun for an exhaust stuck shut...which means the intake can't open against gas pressure during overlap, and something breaks or bends on that side.
I got ahold of my Grandpa's tools, he worked for several aircraft manufacturers in the 40's-70's as a parts quality control inspector.
The valve measured .489 in both axis in 3 places along the stem with my Grandpa's Micrometer. My el Cheapo digital read .494, Lycoming Table of Limits is .4935-.4945. I'm guessing my Granpa's Mic is off a little, don't think it was calibrated since '74.
I didn't have a ball guage exactly, but this T-Gauge worked (kinda). The top of the guide in 2 axis by the spring was .0498 (with Granpa's Mic that is probably .005 short) was .0498, the middle of the guide in 2 axis was .0491 and my T-guage wouldn't squeeze into the valve seat side of the guide. I believe this gives me the proper clearance of .0040-.0060 between the valve stem and guide as long as the valve seat side of the guide followed the .0005 smaller diameter cone shape of the first 1/2 of the guide.
I still need to clean the carbon out of the guide and "feel" how the valve fits.
The valve measured .489 in both axis in 3 places along the stem with my Grandpa's Micrometer. My el Cheapo digital read .494, Lycoming Table of Limits is .4935-.4945. I'm guessing my Granpa's Mic is off a little, don't think it was calibrated since '74.
I didn't have a ball guage exactly, but this T-Gauge worked (kinda). The top of the guide in 2 axis by the spring was .0498 (with Granpa's Mic that is probably .005 short) was .0498, the middle of the guide in 2 axis was .0491 and my T-guage wouldn't squeeze into the valve seat side of the guide. I believe this gives me the proper clearance of .0040-.0060 between the valve stem and guide as long as the valve seat side of the guide followed the .0005 smaller diameter cone shape of the first 1/2 of the guide.
I still need to clean the carbon out of the guide and "feel" how the valve fits.
